As light, including near-infrared radiation, is finding increasing use as an information carrier in guided-wave telecommunications, there is growing interest in light-sensitive and light-influencing devices, e.g., detectors, modulators, and switches. Such devices are of interest further in computerized image processing and, potentially, in data processing in general. Of particular interest are semiconductor modulator devices based on a so-called quantum-confined Stark effect (QCSE), using a semiconductor quantum well with strong optical absorption at the wavelength of the quantum-well exciton, and with shifting of the exciton energy by means of an electric field. Often, for free-space optics as well as for wave-guided or integrated optics, structures are recommended which include a multitude of quantum wells so as to cumulate their optical effects.
One type of proposed devices, known as self-electro-optic effect devices (SEED), include a multi-quantum-well structure in a p-i-n diode; such devices are disclosed in U.S. Pat. No. 4,546,244, issued Oct. 8, 1985 to D. A. B Miller et al., U.S. Pat. No. 4,754,132, issued Jun. 28, 1988 to H. S. Hinton et al., U.S. Pat. No. 4,800,262, issued Jan. 24, 1989 to A. L. Lentine et al., and U.S. Pat. No. 4,959,534, issued Sep. 25, 1990 to A. L. Lentine et al., and they are the subject, e.g., of papers by D. A. B. Miller et al., "Novel Hybrid Optically Bistable Switch: The Quantum Well Self-electro-optic Effect Device", Applied Physics Letters 45 (1984), pp. 13-15, D. A. B. Miller et al., "Integrated Quantum Well Self-electro-optic Effect Device: 2.times.2 Array of Optically Bistable Switches", Applied Physics Letters 49 (1986), pp. 821-823, D. A. B. Miller, "Quantum Wells for Optical Information Processing", Optical Engineering 26 (1987), pp. 368-372, A. L. Lentine et al., "Symmetric Self-electro-optic Effect Device: Optical Setreset Latch", Applied Physics Letters 52 (1988), pp. 1419-1421, A. L. Lentine et al., "Symmetric Self-electrooptic Effect Device: Optical Set-reset Latch, Differential Logic Gate, and Differential Modulator/Detector", IEEE Journal of Quantum Electronics 25 (1989), pp. 1928-1936, and M. E. Prise et al., "Module for Optical Logic Circuits Using Symmetric Self-electrooptic Effect Devices", Applied Optics 29 (1990), pp. 2164-2170. Similar structures have been proposed as intensity modulators, phase modulators, and Mach-Zehnder interferometers for wave-guided optics; see, e.g., S. K. Korotky et al., "Optical Intensity Modulation to 40 GHz Using a Waveguide Electro-optic Switch", Applied Physics Letters 50 (1987), pp. 1631-1633, K. Wakita et al., "High-speed Electrooptic Phase Modulators Using InGaAs/InAlAs Multiple Quantum Well Waveguides", IEEE Photonics Technology Letters 1 (1989), pp. 441-442, J. E. Zucker et al., "Miniature Mach-Zehnder InGaAsP Quantum Well Waveguide Interferometers for 1.3 .mu.m", IEEE Photonics Technology Letters 2 (1990), pp. 32-34, and J. E. Zucker et al., "Optical Waveguide Intensity Modulators Based on a Tunable Electron Density Multiple Quantum Well Structure", Applied Physics Letters 56 (1990), pp. 1951-1953.
In another line of investigation, electrical and optical effects have been studied extensively in quantum-well structures based on resonant-tunneling principles, the following being cited here as representative: L. L. Chang et al., "Resonant Tunneling in Semiconductor Double Barriers", Applied Physics Letters 24 (1974), pp. 593-595, B. Ricco et al., "Physics of Resonant Tunneling. The One-dimensional Double-barrier Case", Physical Review B 29 (1984), pp. 1970-1981, U.S. Pat. No. 4,849,799, issued Jul. 18, 1989 to F. Capasso et al., U.S. Pat. No. 4,872,744, issued Oct. 10, 1989 to J. H. Abeles et al., I. Mehdi et al., "Novel Use of Resonant Tunneling Structures for Optical and IR Modulation", Superlattices and Microstructures 5 (1989), pp. 443-449, I. Bar-Joseph et al., "Differential Absorption Spectroscopy of Charge Distributions in Double-barrier Tunnel Structures", Physical Review B 41 (1990), pp. 3264-3267, and M. Wegener, "Absorption and Refraction Spectroscopy of a Tunable-electron-density Quantum-well and Reservoir Structure", Physical Review B 41 (1990), pp. 3097-3104.
The invention described in the following is motivated by the desire for fast-acting microminiature optical switches, modulators, and oscillators which are particularly suited for inclusion in integrated-optics structures.